The present invention relates to stimulators including stimulating coils constructed and intended for the magnetic stimulation of neuro-muscular tissue by inducing electric currents in such tissue
Stimulating apparatus of the kind mentioned commonly includes means for applying at least one current pulse and preferably a series of current pulses to a coil, which may be a simple circular coil, or a figure of eight coil or be a coil with a plurality of turns forming the pulse generating apparatus for use with such a coil is well known and is described for example in GB Patent number 2298370 and European Patent EP-0692993.
It is customary practice to wind stimulating coils as a single layer on or in a non magnetic support so that all the coil can be disposed as closely as possible to the tissue that is to be stimulated. The coil is in essence apart from any insulating coating which is normally required owing to the high voltages and currents disposed in air, so that the magnetic field produced when current flows through the coil is all in a region of high reluctance.
The present invention is based on the provision of a body of ferromagnetic material, preferably highly permeable low reluctance material, disposed adjacent one broad side of the coil, i.e. the rear of the coil The material of the body is preferably selected to provide a highly permeable block with low eddy current loss, and may comprise sintered iron powder.
Reference will be made hereinafter to the accompanying drawings, in which